It is known that aldehydes can be prepared according to the general scheme (1) by the Oxo-synthesis which comprises hydroformylating olefins or olefinic compounds with carbon monoxide and hydrogen in the presence of a cobalt catalyst: ##STR1##
It is also known to prepare aldehydes branched at the second or alpha carbon by aldolization in alkaline medium, followed by dehydration or crotonization according to scheme (2), starting with two straight-chained aldehyde molecules, a straight-chained plus a branched aldehyde, or two branched aldehydes with the condition that at least one of the two reacting aldehydes is not branched at the alpha carbon. All these starting aldehydes can be obtained by Oxo-synthesis. ##STR2##
The branched aldehydes formed according the scheme (2) can be transformed by hydrogenation in liquid phase according to scheme (3). ##STR3##
In the schematic equations (1), (2) and (3) the R's represent any straight or branched alkyl group.
Hydroformylation of olefinic hydrocarbons according to scheme (1) is exemplarily effected in the presence of cobalt carbonyl catalyst under pressures from about 100 to 300 bars and at temperatures in the range of from about 100.degree. to 200.degree. C. using a mixture of hydrogen and carbon monoxide with molar ratio H.sub.2 /CO in the range of from about 1.1/1 to 1.5/1, usually obtained by gaseous cracking of methane. The Oxo reaction requires a well-controlled ratio of H.sub.2 /CO in order to ensure stability of the cobalt carbonyl which necessitates a partial pressure of CO sufficient to prevent its decomposition.
The preparation of the necessary gaseous mixture of hydrogen and carbon monoxide therefore requires a special gas-cracking treatment which comprises first separating the components from each other either by physical means at low temperatures around -50.degree. C. or by chemical means. The separated carbon monoxide and hydrogen are then combined in a ratio suitable for the Oxo process and the excess hydrogen can serve to hydrogenate the aldehydes to alcohols. The preliminary treatment necessitates accessory installations which are complex and burdensome.